(a) Field of the Invention
This invention relates to a novel two-step process for the preparation of 3,3-bis(phenyl)phthalides useful in the art of carbonless duplicating as, for example, in pressure-sensitive systems and in thermal marking systems and to a novel process for the preparation of 2-[bis(phenyl)methyl]-benzoic acid intermediates to said phthalides.
(b) Description of the Prior Art
It is well established in the dyestuff art that benzaldehyde condenses with two equivalents of aniline in the presence of an acidic material, for example, sulfuric acid to form diaminotriphenylmethane. Similarly, the condensation of p-aminobenzaldehyde with two equivalents of aniline yields leuco Pararosaniline, 4,4',4"-triaminophenylmethane. And in an analgous reaction leuco crystal violet, 4,4',4"-tris(dimethylaminophenyl)methane is obtained from the interaction of p-dimethylaminobenzaldehyde with two equivalents of N,N-dimethylaniline in the presence of an acidic material. On the other hand, the chemical moiety known as 3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide, commonly known as Crystal Violet Lactone or simply CVL is prepared by a number of synthetic routes. One such route is the multi-step synthesis in which Michler's hydrol, 4,4'-dimethylaminobenzhydrol, is reacted with 3-dimethylaminobenzoic acid in the presence of sulfuric acid to obtain 2-[bis(4-dimethylaminophenyl)methyl]-5-dimethylaminobenzoic acid which is isolated. Then said isolated benzoic acid is oxidized in a second step to obtain the phthalide known as CVL. However, the Michler's hydrol used as an intermediate in the process for preparing CVL is itself, prepared by a two-step synthesis. In the first step, two equivalents of N,N-dimethylaniline and formaldehyde are interacted to obtain Michler's methane which is isolated. In the second step, Michler's methane is oxidized with lead dioxide to obtain Michler's hydrol.
In a second synthetic route to CVL, which is also a multi-step synthesis, 4-dimethylaminobenzaldehyde is reacted with 3-dimethylaminobenzoic acid to obtain 3-(4-dimethylaminophenyl)-6-dimethylaminophthalide in the first step. In a second step, the 3-(4-dimethylaminophenyl)-6-dimethylaminophthalide from step one is interacted with N,N-dimethylaniline in the presence of a Friedel-Crafts type catalyst to obtain 2-[bis(4-dimethylaminophenyl)methyl]-5-dimethylaminobenzoic acid. In a third step, the benzoic acid from step two is oxidized to obtain 3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide.
In another known process for the preparation of CVL there are three steps. The first step comprises the interaction of the methyl ester of 2-formyl-5-dimethylaminobenzoic acid with two equivalents of N,N-dimethylaniline to obtain the methyl ester of 2-[bis(4-dimethylaminophenyl)-methyl]-5-dimethylaminobenzoic acid. After isolation, this benzoic acid is oxidized in the second step and finally in the third step the oxidized product is saponified and the lactone ring is closed to obtain the 3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide (CVL).
In all of these art-known processes there are a multiple of synthetic steps required usually with isolation of the intermediate material after each of the steps. In addition, many of the starting materials required for these processes themselves have to be made by processes involving one or more synthetic steps. Each step required increases the cost of the final desired product, uses additional valued raw materials and increases the disposal problems of both the liquid and solid wastes from the overall synthetic processes.
The following items to date appear to constitute the most relevant prior art with regard to the instant invention.
U.S. Pat. No. 2,417,897 and its corresponding U.S. Reissue Pat. No. 23,024, which issued Mar. 25, 1947 and Aug. 17, 1948, respectively, disclose a three-step process for the preparation of 3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide, Crystal Violet Lactone (CVL). In the first step, 3-dimethylaminobenzoic acid is prepared from 3-aminobenzoic acid by alkylating the free amine using methyl iodide in the presence of potassium hydroxide. In the second step, the 3-dimethylaminobenzoic acid is condensed with 4,4'-bis(dimethylamino)benzhydrol in the presence of sulfuric acid to obtain 2-[bis(4-dimethylaminophenyl)methyl]-5-dimethylaminobenzoic acid. In the third step, the 2-[bis(4-dimethylaminophenyl)methyl]-5-dimethylaminobenzoic acid is oxidized using lead dioxide in dilute hydrochloric acid to obtain the CVL.
U.S. Pat. No. 4,045,458, which issued Aug. 30, 1977 discloses a process for the preparation of 2-[bis(4-dialkylaminophenyl)methyl]-5-dialkylaminobenzoic acids by condensing a 3-(4-dialkylaminophenyl)-6-dialkylaminophthalide with an N,N-dialkylaniline in the presence of a Friedel-Crafts type catalyst. The patent further discloses a process in which the 2-[bis(4-dialkylaminophenyl)methyl]-5-dialkylaminobenzoic acid obtained in the above process can be oxidized utilizing various oxidizing agents to obtain 3,3-bis(4-dialkylaminophenyl)-6-dialkylaminophthalides.
In the fourth Edition of Beilsteins Handbuch der Organische Chemie, Vol. 14, page 549, 4,4"-bis-dimethylaminotriphenylmethanecarbonsaure-(2) is reported as a by-product in the preparation of 3-(4-dimethylaminophenyl)phthalide by the condensation of dimethylaniline with o-phthalaldehydic acid in the presence of a catalyst such as zinc chloride, phosphorous oxychloride or potassium bisulfate.
U.S. Pat. No. 3,971,821, issued July 27, 1976, discloses a three-step process for the preparation of 3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide which comprises in the first step reacting the methyl ester of 2-formyl-5-dimethylaminobenzoic acid with two molecular equivalents of N,N-dimethylaniline to obtain the methyl ester of 2-[bis(4-dimethylaminophenyl)methyl]-5-dimethylaminobenzoic acid which in turn is oxidized in a second step and the oxidized product is saponified in the third step to obtain the 3,3-bis(4-dimethylaminophenyl)-6-dimethylaminophthalide (CVL).
U.S. Pat. No. 3,995,088, issued Nov. 30, 1976, discloses a process for the preparation of leuco methylene dyestuffs which involves the reaction of two molecular equivalents of a substituted N,N-dialkylaniline with one molecular equivalent of a benzaldehyde in the presence of an acidic substance and optionally having urea present during the reaction.